Friedrich Lackner

Development of MQXF: The Nb 3 Sn Low-

The High Luminosity (HiLumi) Large Hadron Collider (LHC) project has, as the main objective, to increase the LHC peak luminosity by a factor five and the integrated luminosity by a factor ten. This goal will be achieved mainly with a new interaction region layout, which will allow a stronger focusing of the colliding beams. The target will be to reduce the beam size in the interaction points by a factor of two, which requires doubling the aperture of the low-β (or inner triplet) quadrupole magnets. The use of Nb3Sn superconducting material and, as a result, the possibility of operating at magnetic field levels in the windings higher than 11 T will limit the increase in length of these quadrupoles, called MQXF, to acceptable levels. After the initial design phase, where the key parameters were chosen and the magnets conceptual design finalized, the MQXF project, a joint effort between the U.S. LHC Accelerator Research Program and the Conseil Européen pour la Recherche Nucléaire (CERN), has now entered the construction and test phase of the short models. Concurrently, the preparation for the development of the full-length prototypes has been initiated. This paper will provide an overview of the project status, describing and reporting on the performance of the superconducting material, the lessons learnt during the fabrication of superconducting coils and support structure, and the fine tuning of the magnet design in view of the start of the prototyping phase.

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A key challenge for a future circular collider (FCC) with centre-of-mass energy of 100 TeV and a circumference in the range of 100 km is the development of high-field superconducting accelerator magnets, capable of providing a 16 T dipolar field of accelerator quality in a 50 mm aperture. This paper summarizes the strategy and actions being undertaken in the framework of the FCC 16 T Magnet Technology Program and the Work Package 5 of the EuroCirCol.

Quadrupole for the HiLumi LHC

The upgrade of the Large Hadron Collider (LHC) collimation system includes additional collimators in the LHC lattice. The longitudinal space for these collimators will be created by replacing some of the LHC main dipoles with shorter but stronger dipoles compatible with the LHC lattice and main systems. The project plan comprises the construction of two cryoassemblies containing each of the two 11-T dipoles of 5.5-m length for possible installation on either side of interaction point 2 of LHC in the years 2018-2019 for ion operation, and the installation of two cryoassemblies on either side of interaction point 7 of LHC in the years 2023-2024 for proton operation. The development program conducted in conjunction between the Fermilab and CERN magnet groups is progressing well. The development activities carried out on the side of Fermilab were concluded in the middle of 2015 with the fabrication and test of a 1-m-long two-in-one model and those on the CERN side are ramping up with the construction of 2-m-long models and the preparation of the tooling for the fabrication of the first full-length prototype. The engineering design of the cryomagnet is well advanced, including the definition of the various interfaces, e.g., with the collimator, powering, protection, and vacuum systems. Several practice coils of 5.5-m length have been already fabricated. This paper describes the overall progress of the project, the final design of the cryomagnet, and the performance of the most recent models. The overall plan toward the fabrication of the series magnets for the two phases of the upgrade of the LHC collimation system is also presented.

The 16 T Dipole Development Program for FCC

The high-luminosity large hadron collider (LHC) project at CERN entered into the production phase in October 2015 after the completion of the design study phase. In the meantime, the development of the 11 T dipole needed for the upgrade of the collimation system of the machine made significant progress with very good performance of the first two-in-one magnet model of 2-m length made at CERN. The 11 T dipole, which is more powerful than the current main dipoles of LHC, can be made shorter with an equivalent integrated field. This will allow creating space for the installation of additional collimators in specific locations of the dispersion suppressor regions. Following tests carried out during heavy ions runs of LHC in the end of 2015, and a more recent review of the project budget, the installation plan for the 11 T dipole was revised. Consequently, one 11 T dipole full assembly containing two 11 T dipoles of 5.5-m length will be installed on either side of interaction point 7. These two units shall be installed during the long shutdown 2 in years 2019–2020. After a brief reminder on the design features of the magnet, this paper describes the current status of the development activities, in particular the short model programme and the construction of the first full scale prototype at CERN. Critical operations such as the reaction treatment and the coil impregnation are discussed, the quench performance tests results of the two-in-one model are reviewed and finally, the plan toward the production for the long shut down 2 is described.

The 11 T Dipole for HL-LHC: Status and Plan

The upgrade of the LHC collimation system includes additional collimators in the LHC lattice. The longitudinal space for the collimators can be obtained by replacing some LHC main dipoles with shorter but stronger dipoles compatible with the LHC lattice and the existing powering circuits, cryogenics, and beam vacuum. A joint development programme aiming at building a 5.5 m long two-in-one aperture Nb3Sn dipole prototype suitable for installation in the LHC is being conducted by FNAL and CERN. As part of the first phase of the programme, 1 m and 2 m long single aperture models are being built and tested. Later on, the collared coils from these models will be assembled and tested in a two-in-one aperture configuration in both laboratories. A 2 m long practice model made of a single coil wound with Nb3Sn cable, MBHSM101, was developed and constructed at CERN. It has been completed, and tested at both 4.3 K and 1.9 K. This practice model features collared coils based on removable pole concept, S2-glass cable insulation braided over a mica layer, and coil end spacers made of sintered stainless steel with springy legs. The paper describes the main features of this practice model, the main manufacturing steps and the results of the cold tests.

Progress on the Development of the Nb3Sn 11T Dipole for the High Luminosity Upgrade of LHC

As a part of the large hadron collider luminosity upgrade (HiLumi-LHC) program, CERN is planning to replace some of the 8.33-T 15-m-long Nb-Ti LHC main dipoles with shorter 11 T Nb3Sn magnets providing longitudinal space for additional collimators. Whereas the present design of the 11 T dipole enables the use of RRP conductor with critical current degradation after cabling at the level of 5%, new cross sections of the cable have been studied in order to further decrease the degradation of both critical current and resistivity of the copper matrix. This change is particularly beneficial for the PIT conductor. The coil layout is reoptimized to accommodate the new cable geometry, using the ROXIE code. A set of additional design changes are implemented, such as reduction of the outer yoke diameter. In this paper, we review the main parameters of the present design, describe the changes implemented in the new design, and discuss their impact on both the electromagnetic and structural properties.

Design, Assembly, and Test of the CERN 2-m Long 11 T Dipole in Single Coil Configuration

In 2013, a long shutdown of the Large Hadron Collider at CERN will allow comprehensive maintenance plus consolidation of the machine components, in particular of the 13 kA circuits that feed the main superconducting magnets around the 27-km ring. This shutdown will prepare the accelerator for operation at nominal energy, 14 TeV, with adequate margin on the critical performance parameters. An essential part of the consolidation program consists of adding to the 13 kA splices of the magnet interconnects a copper shunt of high RRR(> 300) that will carry the current in the event of a busbar quench. An important R&D program was conducted in 2010 to design a sound solution for the shunt and for an improved insulation system. The development of the insulation system has required iterations aiming at an adequate solution. The functional requirements for the insulation are a breakdown voltage of at least 3.1 kV in superfluid helium and sufficient mechanical strength to withstand stresses of the order of 50 MPa. The insulation system shall provide mechanical restraint for the shunted splices so that their transversal deflection is limited to 0.25 mm. This paper describes the final design of the insulation and the optimization process. The results from dielectric tests and numerical optimization of the insulation cover will be also presented. Finally, the performance of the new insulation will be compared to the previous version.

Design Optimization of the Nb3Sn 11 T Dipole for the High Luminosity LHC

In the long LHC (Large Hadron Collider) shutdown in 2013 it is foreseen to intervene on all the 13 kA interconnections in order to guarantee the necessary margin and redundancy to provide safe LHC operation at 7 TeV per beam. This implies reinforcement of the present interconnection configuration including a new insulation scheme of the busbars. The purpose of the new insulation model is to provide dielectric insulation with at least the same performance as its predecessor currently installed in the LHC machine, but in addition to contain the Lorentz forces. This paper describes the analytic and empirical approach of development to reach a new insulation concept based on state of the art materials and manufacturing techniques.

An Improved Insulation System for the LHC Main 13 kA Interconnection Splices

A next step of energy increase of hadron colliders beyond the LHC requires high-field superconducting magnets capable of providing a dipolar field in the range of 16 T in a 50-mm aperture with accelerator quality. These characteristics could meet the requirements for an upgrade of the LHC to twice the present beam energy or for a 100-TeV center of mass energy future circular collider. This paper summarizes the activities and plans for the development of these magnets, in particular within the 16 T Magnet Technology Program, the WP5 of the EuroCirCol, and the U.S. Magnet Development Program.

Development of a New Insulation Approach for the LHC Main 13 kA Interconnection Splices

The High-Luminosity upgrade of the Large Hadron Collider at CERN comprises the implementation of a new generation of high-field superconducting quadrupole and dipole magnets. The dipole fields of up to 12.1 T at nominal current require the use of high-critical-current Nb3Sn strand for the fabrication of the coils. These coils will be up to 8 m long and represent the longest Nb3Sn coils so far fabricated for operation accelerator magnets. This brittle A15 phase material requires coil winding prior formation of the superconducting material. The development program at CERN includes the construction of 2-m-long models and full-length prototypes by the wind-and-react technique. The process time and temperature uniformity are stringent during heat treatment and performed inside an EN 1.4841 (AISI Type 314) stainless-steel retort furnace with turbulent flow of Ar atmosphere. During the process, the coil is supported inside a reaction fixture made from 316LN. This paper presents temperature uniformity measurements and results from numerical simulations. The goal is to further improve the heat transfer in combination with turbulent flow generated by a ventilation system. This allows optimizing control parameters for improved heat performance during both the ramping and the dwell time.